Because of the growing cost, scarcity and hazards associated with the use of fossil and nuclear fuels, increasing use is being made of photovoltaic energy sources. Photovoltaic cells are reliable, silent in operation, and neither consume natural resources nor emit polluting byproducts during operation. Initially, photovoltaic power sources were restricted to single crystal devices. These cells were expensive, fragile and bulky; hence, their uses were limited to highly specialized applications.
More recently, thin film electronic devices, including photovoltaic devices, have been developed which are equivalent, or superior, to single crystalline devices in operation. Thin film photovoltaic devices are rugged,
reliable, inexpensive and efficient. U.S. Pat. Nos. 4,226,898 and 4,217,374 of Ovshinsky et al detail techniques for the manufacture of high quality thin film semiconductor materials and devices. Further, techniques have been developed for the large scale, continuous deposition of high quality, thin film photovoltaic devices over relatively large area substrates. Such techniques are disclosed, for example, in U.S. Pat. No. 4,485,125.
Thin film photovoltaic devices may be fabricated from a variety of materials including silicon alloys, germanium alloys, cadmium telluride, copper indium diselinide and other such materials. These devices are thin and flexible and may be readily cut to a variety of sizes and shapes. Thin film photovoltaic devices may be interconnected in a variety of configurations to provide appropriate voltage and power outputs for particular applications. In general, thin film photovoltaic devices are encapsulated between protective layers prior to use, in order to protect them from mechanical damage or ambient atmospheric conditions. Additionally, thin film photovoltaic devices are frequently laminated to relatively rigid support members for particular applications. For example, photovoltaic roofing panels are manufactured by laminating a thin film photovoltaic device to sheets of aluminum, galvanized steel or other such roofing material.
In general, the photovoltaic device is laminated between a protective, transparent top coat and a supporting substrate by means of a layer of thermoplastic polymer or the like and the lamination process is carried out by a vacuum lamination process. Typically, the device is sandwiched between encapsulating layers and a flexible, air impermeable membrane is placed over the device. Air is evacuated from beneath the membrane and the pressure of the atmosphere, acting through the membrane, compresses the device. The device is heated while under compression to complete the lamination. While the results of such lamination are generally adequate, the lamination process represents a significant expenditure of capital resources and the lamination equipment occupies large areas of valuable floor space in a manufacturing environment. Additionally, particular skill in operation of the lamination equipment is necessary.
U.S. patent application Ser. No. 590,775, now abandoned, discloses a process for preparing a substrate for electronic devices, which substrate comprises a metallic support having a layer of electrically insulating, polymeric material laminated thereto. According to the method disclosed therein, the metallic substrate and the insulating polymeric material are interwound to form a tightly wound roll which is then heated. The heat bonds the insulating material to the metal, thereby creating a composite substrate.
The present invention is directed to a process whereby an interleaved assemblage of photovoltaic cells and flexible encapsulating materials is rolled together and laminated with or without an evacuation step. The method of the present invention is simple and inexpensive and may be readily integrated with techniques for the continuous production of large area photovoltaic devices. These and other advantages of the present invention will be readily apparent from the drawings, discussion and description which follow.